The broad division in trenchless pipeline rehabilitation is between liner systems, which involve placing a liner or a new pipe inside an existing old pipe which is to be renewed, and trenchless replacement methods by which an old pipe is replaced by a new one of a size equal to or greater than that of the original pipe. This invention relates particularly to the latter type application.
Replacement methods differentiate between pipe bursting methods, whereby the old pipe is destroyed or broken up underground prior to laying of the new pipe and pipe-extraction methods where the old pipe is removed from underground before laying the new pipe.
In the pipe bursting method a tool which is of greater outer diameter than both the internal diameter of the old pipe and the outer diameter of the new pipe is advanced along the inside of the old pipe whilst towing the new pipeline behind it. This breaks up the old pipe driving the fragments into the surrounding soil and creates a tunnel into which the new pipe is installed. The pipe bursting method can be readily employed to replace old ceramic, asbestos, cement or concrete sewer lines, i.e. any pipeline made of a friable material.
In the pipe extraction method the old pipe is not broken up but is removed from the pipe zone under ground before installation of the new pipe. Pipe extraction is used to replace metal pipelines which are not amenable to pipe bursting and where the extraction has the advantage that metal shards are not left behind in the ground to damage the new pipeline being installed.
It is an object of the present invention to provide a pipe replacement system which can be used in both the pipe bursting and pipe extraction methods.